Light source of controllable intensity



A. J. BARACKET LIGHT SOURCE OF CONTROLLABLE INTENSITY Aug. 31, 1965Filed 5610i. 5, l1963 INVENTOR. Aaser J. BAMc/cr BY om vwd WOP/vers tothe planes of the two members.

3,204,091 LIGHT SOURCE F 'CONTROLLABLE INTENSITY Albert J. Baracket,Cedar Grove, NJ., assigner to Dia mond Power-Specialty Corporation,Lancaster, Ohio, a corporation 'of Ohio Filed Sept. 5, 1962, Ser. No.221,464

3 Claims. (Cl. 24d-20) This invention relates to a light source havingmeans for varying the intensity of the light without changing its colortemperature. In particular it relates to a light 4` source forilluminating photographic slides and the like with substantially uniformand controllable intensity over the face of the slide.

VIn testing television cameras and in presenting photon graphic slidesfor television program material it is desirable to provide an even fieldof illumination and to have some means for varying the intensity ofillumination. An electric light must'be used to furnish theillumination, but any attempt to change the intensityby varying thevoltage ormcurrent supplied to the light results in a change in colortemperature, if the light is produced by an incandescent bulb, or inerratic operation if the light is produced by other means. A change incolor temperature particularly for color slides or color televisioncannot be tolerated.

In accordance with this invention a light box is provided which is openon one side so that an object to be examined, `such as a photographicslide, may be placed over this side. Within the box and at some distancefrom the open side is a source of light and between the source and theopen 'side are two foraminous members, one of which is movable relativeto the other to change the alignment of the foraminations, or aperturesin the two members to change the overall opacity o f the members. Adiffusing member is placed between the open side and the foramnousmembers to assist in making the light uniform over the entire area to beilluminated.

The invention will be described in greater detail in the followingspecification together with the drawing in which:

FIG.y 1 is a perspective view of a light source constructed according tothe invention and with parts broken away to show the interior thereof;

FIG. 2 shows a cross-sectional view of the light source of FIG. 1 toclarify the arrangement of parts therein.

In FIG. 1 the box is defined by a top 11, a side 12, a rear side 13, anda bottom 14. The front is open except for edges 16 and 17 extendinginwardly from the sides and an edge 18 extending upwardly from thebottom. These edges cooperate with a downwardly turned lip 19 toform aslot for receiving the slide `21 to be illuminated. Directly behind theslide 21 is a diffusing member 22, which, in. this embodiment, is aflat, translucent plate, and is placed there to disperse the lightpassing through it so as to assist in breaking up any hot spots ofillumination.

`Behind the diffusing member 22 are two foraminous, opaque members 23and 24, the rst of which is located in axed position directly across thepath of light to the slide 21, and the other of which is parallel to thefirst but is movable with respect thereto in a direction parallel Bothmembers are flat plates in the embodiment shown and the movable member24 slides in guides 26 and 27 extending from the side 12. A similar pairof guides, not shown in this view,

extends from the opposite side of the box.

The movable member 24 is connected to a threaded rod 28 which turns in acorrespondingly threaded apertureA in the top 11 to raise and lower themember. If desired, one or more springs, such as spring 29, may beplaced beneath the member 24 to assist in raising itand, by exertingpressure on the member` at all times, to smooth out its motion. This,coupled with a fine pitch on the threaded rod 28 permits accuratecontrol of the motion of member 24 and hence of the rela'tivealgnment`tubes, of which only one tube 33 appears inthis figure.l ln order toutilize as much ofthe light as possible, and

in order to spread the available illumination as revenly as possible,the innersurfaces of the rear 13, as well as the rear portions of theside 12 andthe opposite, unshown side, and the top 11 and bottom 14 aremade reiiective. While this could be done by silvering these surfaces,to do so would probably createv concentrated areas of illumination, orhot spots, and it is better to make these surfaces white.

FIG. 2 shows a preferred arrangement of three fluorescent tubes 33-35.These tubes are parallel to each other and substantially eguidistantfrom the slide 21, which means that the tubes 33-35 lie in a planeparallel to the plane of the slide. Having three tubes contributes tothe diffusing member 22 also contributes to the same effect.

In the event that a residual unevenness remains, it may v besubstantially completely eliminated by so spacing the apertures in theforaminous members that less light will be able to pass through thosesections which would otherwise have the most light. The same effect maybe obtained by making the aperturesof different sizes and keep-` ingthem evenly spaced. Typically, it is to be expected that slightlygreater light intensity would be present directly in front of each ofthe tubes. 33-35, and sopas shown in FIG. 1 the apertures in suchlocations may be slightly smaller.

It must be noted however, that it would be undesirable so to arrange theapertures that the illumination would be reduced more quickly in onearea than another. This may be avoided by elongating the apertures ofplate 23 in a direction parallel to the motion of plate 24. In such casethe apertures in the plate 24 may be elongated in the perpendiculardirection. Of course, the arrangement of apertures specified for plate23 and the arrangement for plate 24 may be reversed since, normally, themovement of plate 24 from the position of greatest, or even total,opacity to greatest transparency may be very minute if the apertures arecorrespondingly small. 1

While this invention has been described in the specific terms of asingle embodiment, it will be recognized that other forms may beconstructed without departingfrom the true scope of the invention asdened by the following claims.,

What is claimed is: i i

1. A light source comprising: a fiat diffusing plate; a luminous elementspaced from one `surface thereof to direct light therethrough; opaquemeans extending from the edges of said plate and enclosing a volume thatlin` Patented Aug. 3l, 1965 ing the intensity of light reaching saidsheet from said luminous element; and means to move one of said sheetswith respect to the other to vary the relative alignment offoraminations in said sheets thereby to vary the overall intensity oflight passing through said sheets without varying the relative intensityof various color components of the light.

2. A light source comprising: a at diffusing plate; a luminous elementspaced from one surface thereof t direct light therethrough; opaquemeans extending from the edges of said plate and enclosing a volume thatincludes said luminous element, the inner surface of said opaque meansbeing reflective to increase the apparent intensity of said luminouselement; a pair of foraminous sheets of opaque material located acrossthe light path between said luminous element and said diffusing plate sothat the light travelling along said path strikes said sheets, one ofsaid sheets having foraminations with varying space-size parameterssubstantially complementi ing the intensity of light reaching said sheetfrom said luminous element, the other of said sheets havingforaminations with uniform space-size parameters, and means to move theother of said sheets with respect to said one sheet to vary the relativealignment of foraminations in said sheets thereby tovary the overallintensity of light passing through said sheets without varying therelative intensity of various color components of the light.

3'. A light source comprising: a at, diffusing plate; a plurality ofuorescent lights lying in a plane spaced from Cil said plate andparallel thereto to direct light -therethroughjy opaque means extendingfrom the edges of said plate and enclosing a volume that includes saidlights, saidv opaque means having a reective surface facing said lightsto increase the apparent intensity thereof; a first opaque, stationary,foraminous sheet across the path of light from said lights to saiddiffusing plate; a second opaque, movable, foraminous sheet across thepath of,Y light from said lights to said diffusing plate, one of saidReferences Cited by the Examiner UNITED STATES PATENTS 2,213,382 9/40Busse 95--73 2,300,970 11/42 Riess et al. 88--24 2,676,409 4/54 Gamble33-1 2,971,447 2/ 61 Debrie 95-73 NORTON ANSI-IER, Primary Examiner.

EVON C..BLUNK, Examiner.

1. A LIGHT SOURCE COMPRISING: A FLAT DIFFUSING PLATE; A LUMINOUS ELEMENTSPACED FROM ONE SURFACE THEREOF TO DIRECT LIGHT THERETHROUGH; OPAQUEMEANS EXTENDING FROM THE EDGES OF SAID PLATE AND ENCLOSING A VOLUME THATINCLUDES SAID LUMINOUS ELEMENT, THE INNER SURFACE OF SAID OPAQUE MEANSBEING REFLECTIVE TO INCREASE THE APPARENT INTENSITY OF SAID LUMINOUSELEMENT; A PAIR OF FORAMINOUS SHEETS OF OPAQUE MATERIAL LOCATED ACROSSTHE LIGHT PATH BETWEEN SAID LUMINOUS ELEMENT AND SAID DIFFUSING PLATE SOTHAT THE LIGHT TRAVELLING ALONG SAID PATH STRIKES SAID SHEETS, ONE OFSAID SHEETS HAVING FORAMINATIONS WITH VARYINS SPACE-SIZE PARAMETESSUBSTANTIALLY COMPLEMENTING THE INTENSITY OF LIGHT REACHING SAID SHEETFROM SAID LUMINOUS ELEMENT; AND MEANS TO MOVE ONE OF SAID SHEETS WITHRESPECT TO THE OTHER TO VARY THE RELATIVE ALIGNMENT OF FORAMINATIONS INSAID SHEETS THEREBY TO VARY THE OVERALL INTENSITY OF LIGH PASSINGTHROUGH SAID SHEETS WITHOUT VARYING THE RELATIVE INTENSITY OF VARIOUSCOLOR COMPONENTS OF THE LIGHT.